Oh, ok. I didn't really know that, sorry.
What breed, age is he? Has he been trained alot?
There are a lot of factors to consider with a "hyper" horse like:
- how old is he?
- what does he eat? (maybe his grain makes him hot)
- is he hyper in the pasture / stall / lunge line, etc. or just in the arena?
- has he been poorly trained?
- is his tack fitting properly? (ill-fitting tack will definitely cause this kind of thing)
- do his teeth need to be done? (I've seen a horse act completely nuts because her teeth needed to be done. She was the calmest thing after that)
Is there any reason other than just bad behavior why he may be acting this way?
Sometimes all of those reasons are ruled out, and the horse just likes to go fast. My horse gets like this at times too. I try to make things interesting for her, lots of circles, serpentines and bending. Halts and backing are also incredibly helpful.
When your horse speeds up like this, try to THINK slow. I know that sounds weird, but it does work. Think, "slow, sitting trot" or whatever it may be. Sit back, even exaggerate it, and work the horse through its back end, by using lots of leg. Don't pull on his face. Horses tend to go faster when you're yanking on their mouths to slow them down. When your horse starts to speed, turn him into a circle, and keep him in it until he slows down and then start again on the track.
I find its soo helpful to just train YOURSELF to think calmly and slowly. Be very careful of all your movements. Ask him gently, work WITH him, eyes up to plan ahead of you. Put yourself in a frame of mind of slowness and think about working WITH his body movements and not against them. For example, at the posting trot, slow YOUR posting movement, sit back, relax, and this should help slow down HIS trot.
Hope this helps!